1. 1 3 Computing System Fundamentals 3.2 Computer Architecture

2. 3.2.1 The CPU

3. 3 Input – process - output

4. 4 The CPU Central Processing Unit = ‘chip’ = processor The device controlling the computer. It follows a sequence of instructions (the program) in order to carry out particular tasks. It handles calculations and directs data to appropriate memory locations or peripherals.

5. 5 The CPU It has to be able to distinguish between the instructions and the data itself (both of which are in binary form). It applies logical operations (e.g. is A greater than B?) to the bits using relatively simple logic circuits. If the instruction set is kept fairly simple many operations can be carried out very quickly.

6. 6 The CPU The CPU basically has four main components: ‣ the control unit (CU), ‣ the arithmetic and logic unit (ALU), ‣ registers (simple memory locations) and ‣ buses (connections carrying data).

7. 7 The CU The role of the CU: ‣ decoding program instructions, ‣ controlling the sequence in which instructions are executed by the ALU, ‣ controlling access to the main memory store, ‣ regulating the timing and synchronisation of the processor and ‣ sending control signals to and receiving control signals from the peripheral devices.

8. 8 The ALU The role of the ALU: ‣ performing calculations on data, ‣ making logical comparisons between values, ‣ holding the answers to these in operations various registers until they are stored or later in the program.

9. 9 Registers Registers provide: ‣ immediate storage for the results of simple operations, ‣ program counters e.g. for loops. Registers in the ALU that store intermediate results of calculations are called accumulators.

10. 10 Buses Originally the connectors, now the subsystems, that transfer data within the CPU, computer and peripherals. Generally three categories: ‣ data bus, ‣ address bus (memory locations) and ‣ control bus (control signals)

11. 11 The CPU (overview) Control bus